The present invention relates to radiating systems and, more particularly, to improved synthesizer radiating systems enabling efficient use of small high-Q antennas by active control of energy transfer back and forth between an antenna reactance and a storage reactance.
The theory and implementation of Synthesizer Radiating Systems and Methods are described in U.S. Pat. No. 5,402,133 of that title as issued to the present inventor on Mar. 28, 1995. That patent ("the '133 patent") is hereby incorporated by reference.
A basic radiation synthesizer circuit, as described in the '133 patent, which combines transfer circuits in both directions using two switches is shown in FIG. la. This circuit functions as an active loop antenna where the loop antenna L is the high Q inductive load and a capacitor C is used as the storage reactor. The FIG. la circuit uses two RF type switching transistors, shown as switches RC and DC, for rate and direction control, respectively. Because the devices are operated in a switch mode, efficient operation is obtained since, in theory, no instantaneous power is ever dissipated by such devices. A slower switching device, shown as power control switch PC, can be used to add energy to the circuit from the power supply as energy is radiated. The voltage and current sensor terminals VS and CS, respectively, are used to monitor and calculate the total amount of stored energy at any instant in time, while a feedback control circuit is used to maintain the total energy at a preset value through use of the power control switch PC.
In the FIG. la circuit, when the direction control switch is open, energy can be transferred from current through the inductor L to voltage across the capacitor C, as illustrated by the L to C energy transfer diagram of FIG. 1b. With the rate control switch closed, current flows from ground, through diode D1 and L, and back to ground through the rate control switch RC. In the absence of circuit losses, the current would continue to flow indefinitely. When the rate control switch RC is opened, the inductor current, which must remain continuous, flows through diode D2 and charges up the capacitor C. The rate at which C charges up is determined by the switch open duty cycle of the switch RC. The capacitor will charge up at the maximum rate when the switch is continuously open. The charging time constant is directly proportional to the switch open duty cycle of the rate control switch RC.
When the direction control switch DC of FIG. 1a is closed, energy can be transferred from voltage across the capacitor to current through the inductor, as shown in the C to L energy transfer diagram of FIG. 1c. Diode D1 is always back biased and is, therefore, out of the circuit. When the rate control switch RC is closed, the capacitor C will discharge through L, gradually building up the current through L. If the rate control switch is opened, the capacitor will maintain its voltage while the inductor current flows in a loop through diode D2. In this C to L direction transfer mode, the rate is controlled by the switch closure duty cycle of switch RC. The maximum rate of energy transfer occurs when the switch RC is continuously closed. Its operation is the inverse of that in the other direction transfer mode (L to C).
It should be noted that, in either direction, charge or discharge is exponential. Therefore, the rate of voltage or current rise is not constant for a given rate control duty cycle. In order to maintain a constant rate of charging (ramp in voltage or current), it is necessary to appropriately modulate the duty cycle as charging progresses. Duty cycle determinations and other aspects of operation and control of radiation synthesizer systems are discussed at length in the '133 patent (in which FIGS. 1a, 1b and 1c referred to above appear as FIGS. 8a, 8b and 8c).
In theory, since the power which is not radiated is transferred back and forth rather than being dissipated, lossless operation is possible. However, as recognized in the '133 patent losses are relevant in high frequency switching operations, particularly as a result of the practical presence of ON resistance of switch devices and inherent capacitance associated with switch control terminals. While such device properties are associated with very small losses of stored energy each time a switch is closed, aggregate losses can become significant as high switching frequencies are employed. In addition, if small loop antennas are to be employed, for example, antenna impedance may be higher than basic switching circuit impedance levels, necessitating use of impedance matching circuits which may have less than optimum operating characteristics.
Continuing work with synthesizer radiating systems and methods has indicated the desirability of further development and improvement in respect to the above and other aspects of implementation and operation of such systems and methods.
Objects of the present invention are, therefore, to provide new and improved synthesizer radiating systems and methods and subsets thereof, particularly such as provide one or more of the following advantages and capabilities:
reduction of dissipation of stored energy in switch device ON resistance; PA1 reduction of dissipation of energy stored in power switch control circuits; PA1 provision of sequential switching methods; PA1 reduction of dissipation of stored energy via sequential switching circuits; and PA1 reduction of antenna impedance by provision of multi-segment loop radiator systems. PA1 a loop antenna element configured as a plurality of successive loop segments; and PA1 a like plurality of switching circuits each coupled to a different pair of loop segments. Each switching circuit includes power switch devices arranged for controlled activation to transfer energy back and forth from the loop segments to which it is coupled to a portion of said storage capacitance. PA1 first and second driver switch devices in a series arrangement suitable for connection across a potential and having a common point between the driver switch devices; and PA1 an inductive element coupled at one end to such common point and arranged for a second end to be coupled to a control terminal of the selected power switch device for use in changing states thereof between open and closed states. PA1 (a) initially providing one power switch device in an open state with a voltage across it and energy capacitively stored therein (the "open switch"), PA1 (b) initially providing another power-switch device in a closed state (the "closed switch") and coupled to the open switch device so that the state of the closed switch affects the voltage across the open switch, PA1 (c) reducing the voltage across the open switch by changing the state of the closed switch from closed to open, and PA1 (d) changing the state of the open switch from open to closed at a predetermined time after changing the state of the closed switch in step (c).